Oxidation protected separator

ABSTRACT

A battery separator for a lead/acid battery is resistant to oxidation arising from the use of water or acid containing contaminants, for example chromium (Cr), manganese (Mn), titanium (Ti), copper (Cu), and the like. The separator is a microporous membrane including a rubber. The rubber is no more than about 12% by weight of the separator. The rubber may be rubber latex, tire crumb, and combinations thereof. The rubber may be impregnated into the microporous membrane. The microporous membrane may be a microporous sheet of polyolefin, polyvinyl chloride, phenol-formaldehyde resins, cross-linked rubber, or nonwoven fibers. A method for preventing the oxidation and/or extending battery life of the separator is also included.

RELATED APPLICATIONS

This application claims the benefit of and priority to co-pending U.S.patent application Ser. No. 14/200,102 filed Mar. 7, 2014, now U.S. Pat.No.______, which claimed the benefit of and priority to U. S.provisional application No. 61/774,160 filed Mar. 7, 2013, both of whichare incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is directed to a battery separator for lead/acidbatteries being resistant to oxidation arising from the use of waterand/or acid containing contaminants.

BACKGROUND

Oxidation of the separator, e.g., separators for lead/acid batteries,reduces a battery's cycle life, and thereby reduces the effective lifeof the battery. Oxidation causes the embrittlement (measured by, forexample, loss of % elongation) of the separator which leads to partialor complete failure of the battery.

Contaminants typically originate from the water and/or the sulfuric acidadded to a battery, as well as from impurities in the alloys and activematerials that comprise the electrode plates, may cause oxidation. Suchcontaminants typically include the transition metals of the periodictable, for example: chromium (Cr), manganese (Mn), titanium (Ti), copper(Cu), and the like. Contaminant levels (e.g., Cr, Mn, and/or Ti) ofgreater than about 2.0 ppm [2.0 mg/L] are not recommended. Cucontaminants greater than 26 ppm [26 mg/L] are not recommended. Inbatteries without contaminants (e.g., Cr), the separator may have a lifeof about 7 years, but with contaminants (e.g., 5 ppm Cr), the separatordeteriorates in about 6 months.

In some areas of the world, for example, Asia, lead/acid batteries aresold as ‘dry charge’ batteries. These dry charge batteries are purchasedwithout the water/acid included. The dry charge battery has a longershelf life. However, the user may not be careful to fill the batterywith uncontaminated water/acid. The contaminated water/acid will lead tooxidation of the separator and ultimately to battery failure. Thecontaminants in the water/acid may be sourced from the water/acidcontainers, e.g., steel drums.

USPN5221587 discloses the use of latex in the separator to preventantimony (Sb) poisoning of the lead/acid battery. Antimony poisoningdoes not cause separator oxidation; instead, antimony poisoning causeswater loss from the electrolyte. Antimony is sourced from the leadplates (electrodes) of the battery. Antimony is used as an alloyingagent in the lead to improve the manufacture of the plates and the cyclelife of the battery. Those of ordinary skill would not consider theteachings of USPN5221587 in arriving at a solution to the separatoroxidation problem mentioned above.

USPN6242127 discloses the use of cured, porous rubber in a conventionalpolyolefin separator to improve the electrochemical properties (antimonysuppression) of the separator.

SUMMARY OF THE INVENTION

A battery separator for a lead/acid battery is resistant to oxidationarising from the use of water or acid containing contaminants, forexample chromium (Cr), manganese (Mn), titanium (Ti), copper (Cu), andthe like, and combinations thereof. The separator is a microporousmembrane including a rubber. The rubber is no more than about 12% byweight of the microporous membrane. The rubber may be rubber latex, tirecrumb, and combinations thereof. The rubber may be impregnated into themicroporous membrane. The microporous membrane may be a microporoussheet of polyolefin, polyvinyl chloride, phenol-formaldehyde resins,cross-linked rubber, or synthetic nonwoven fibers. A method forpreventing the oxidation of the separator is also included.

DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in thedrawings a form that is presently preferred; it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

FIG. 1 is a graphical comparison of the oxidation resistance, presentedas % elongation as a function of hours, of an inventive separator (B) toother known separators when the separators are subjected to a watercontaining 4.7 ppm chromium (Cr).

FIG. 2 is a graphical comparison of the oxidation resistance, presentedas % elongation as a function of hours, of an inventive separator (G) toother known separators when the separators are subjected to a watercontaining 4.5 ppm chromium (Cr).

DESCRIPTION OF THE INVENTION

Lead/acid batteries are well known, see for example, Linden, Handbook ofBatteries, 2^(nd) Edition, McGraw-Hill, Inc. New York, N.Y. (1995)and/or Besenhard, Handbook of Battery Materials, Wiley-VCH Verlag GmbH,Weinheim, Germany (1999), both incorporated herein by reference. In oneembodiment, the separator, described hereinafter, may be used in alead/acid battery. The battery may be, for example, a flooded, storage,ISS, EFB, carbon, or dry charge lead acid battery with, for example,leaf, piece, pocket, or envelope type or style separators, with orwithout glass mat.

The inclusion of rubber (discussed below) with the separator of thelead/acid battery can prevent, or reduce, oxidation of the separatorcaused by contaminants, such as Cr, Mn, Ti, and the like, and therebyincrease the life cycles of batteries.

Separators, as used herein, refer to microporous membranes. Suchseparators are well known as demonstrated by reference to Besenhard,Handbook of Battery Materials, Wiley-VCH Verlag GmbH, Weinheim, Germany(1999), incorporated herein by reference. Microporous membranes may bemade from: sheets of polyolefin (e.g., polyethylene, polypropylene,ultra high molecular weight polyethylene (UHMWPE), and combinationsthereof), polyvinyl chloride (PVC), phenol-formaldehyde resins(including, for example, cellulosic and/or synthetic impregnated withphenol-formaldehyde resins), crosslinked rubber, or nonwoven (e.g.,inert fibers including cellulosic fibers or glass fibers). In oneembodiment, the microporous membranes may be made from polyethylene,UHWMPE, or a combination of both. In another embodiment, the microporousmembrane is a polyolefin (polyolefin being high molecular weight PEand/or ultra high molecular weight PE)/filler (for example a silicafiller)/processing oil, where the polyolefin/filler/processing oil aremixed and then extruded into a precursor (e.g., a flat sheet), thencalendered to create a profile (e.g., ribs) and then the processing oilis extracted therefrom. The microporous membranes may have a ribbedprofile. The ribs may be conventional, e.g., running in the machinedirection (MD) on the side to the positive electrode (e.g., to, amongother things, separate the separator from the positive electrode, andform gas channels that allow gas to escape and promotes mixing duringover charge conditions), but the ribs may also extend in the crossmachine direction (CMD) on the side to the negative electrode (to retardacid stratification).

Rubber, as used herein, refers to rubber latex, tire crumb, andcombinations thereof. In one embodiment, the rubber may beun-cross-linked or uncured rubber. In another embodiment, the rubberlatex may be natural or synthetic rubber latex. In another embodiment,the rubber may be natural rubber latex. In yet another embodiment, therubber may be tire crumb. Natural rubbers may include, for example, anygrade (e.g., latex grades), such as ribbed smoked sheet, white and palecrepes, pure blanket crepes or re-mills, thick brown crepes or ambers,and flat bark crepes. Natural rubbers may include Hevea rubbers.Synthetic rubbers may include, for example, methyl rubber,polybutadiene, chloropene rubbers, and copolymer rubbers. Copolymerrubbers may include, for example, styrene/butadiene rubbers,acrylonitrile/butadiene rubbers, ethylene/propylene rubbers (EPM andEPDM), and ethylene/vinyl acetate rubbers. Other rubbers may include,for example, butyl rubber, bromobutyl rubber, polyurethane rubber,epichlorhydrin rubber, polysulphide rubber, chlorosulphonylpolyethylene, polynorborene rubber, acrylate rubber, fluorinated rubber,isoprene rubber, and silicone rubber. These rubbers may be used alone orin various combinations.

In one embodiment, the rubber may be impregnated into the microporousmembrane. Impregnated, as used herein, means that the rubber isincorporated into the body of the microporous membrane, and is not alayer formed on the microporous membrane. So, the rubber may be mixed orblended into one or more of the materials used to form the microporousmembrane. The rubber, for example the latex, is still chemically active(i.e., uncured and/or uncross-linked) after extrusion. Thus, the rubberis a component integral with, or distributed within, or uniformlyblended throughout, or intimately blended in the materials of, themicroporous membrane.

The rubber, as described above, may comprise any portion of themicroporous membrane. In one embodiment, the rubber may comprise no morethan about 12% by weight of the microporous membrane when added to theformulation (i.e., the ‘by weight’ of the raw materials beforeextrusion). In another embodiment, the rubber may comprise about 1-12%by weight of the microporous membrane. In another embodiment, the rubbermay comprise about 1.2-6% by weight of the microporous membrane. In yetanother embodiment, the rubber may comprise about 2-4% by weight of themicroporous membrane. In still another embodiment, the rubber maycomprise about 2.5-3.5% by weight of the microporous membrane. Inanother embodiment, the rubber may comprise about 3% by weight of themicroporous membrane.

The microporous membrane may be made in any conventional fashion. Suchprocessing is well known as demonstrated by reference to Besenhard,Handbook of Battery Materials, Wiley-VCH Verlag GmbH, Weinheim, Germany(1999), incorporated herein by reference. For example, in a PE separator(microporous membrane), the rubber, for example the latex, may be mixedwith the processing oil and mixed with the PE during extrusion. Themixture is then extruded into a precursor (i.e., a flat sheet).Thereafter, the precursor is calendered to create a profile, forexample, ribs (as is conventional). Then, the processing oil isextracted from the profiled sheet, thereby creating the microporousmembrane. The microporous sheet may be subjected to further processingsteps as is conventional in the art of making separators for lead/acidbatteries.

EXAMPLES

The following is a comparison of the inventive separators (Samples B &G) to other separators. The separators are compared on basis of %elongation (a measure of embrittlement, conventional testing) versustime (hours). % elongation is measured as set forth in ASTM D882. The PEseparator refers to a conventional separator wherepolyolefin/filler/processing oil are mixed and extruded in to a flatprecursor, calendered to create the profile, and then the processing oilis extracted therefrom, as is known in the art. The difference between4.7 ppm and 4.5 ppm Cr is immaterial.

Sample Separator Comment A PE separator laminated No improvement in Croxidation with synthetic nonwoven resistance B PE separator with 6%Surprising improvement in Cr by weight latex oxidation resistance C PEseparator laminated No improvement in Cr oxidation with glass nonwovenresistance D PE separator highly No improvement in Cr oxidation orientedresistance E PE separator with 15% No improvement in Cr oxidation byweight residual resistance processing oil F PE separator with Noimprovement in Cr oxidation proprietary commercial resistance(alcohol-based) additive for oxidation resistance G PE separator (35%Surprising improvement in Cr reduction of UHMWPE oxidation resistancecontent) with 6% by weight latex

The present invention may be embodied in other forms without departingfrom the spirit and the essential attributes thereof, and, accordingly,reference should be made to the appended claims, rather than to theforegoing specification, as indicating the scope of the invention.

We claim:
 1. A separator suitable for use in a lead acid batterycomprising: a microporous membrane comprising one or more of the groupconsisting of polyolefin, polyvinyl chloride (“PVC”),phenol-formaldehyde resins, uncross-linked or uncured rubber, nonwovenfibers, and combinations thereof; wherein said microporous membrane issuitable for use in an electrolyte comprising water and acid; whereinsaid electrolyte further comprises one or more contaminants, said one ormore contaminants being one or more selected from the group consistingof chromium, manganese, titanium, copper, and combinations thereof. 2.The separator of claim 1, wherein said uncross-linked rubber or uncuredrubber being selected from the group consisting of rubber latex, tirecrumb, and combinations thereof.
 3. The separator of claim 2, whereinsaid uncross-linked or uncured rubber is in an amount of no more thanapproximately 12% by weight of said microporous membrane.
 4. Theseparator of claim 3, wherein said cross-linked rubber or uncured rubberis in an amount of at least approximately 2% by weight of saidmicroporous membrane to approximately 4% by weight of said microporousmembrane.
 5. The separator of claim 1, wherein microporous membranefurther comprises a first set of ribs on a first surface, and a secondset of ribs on a second surface.
 6. The separator of claim 5, whereinsaid first set of ribs are in a machine direction relative to saidmicroporous membrane.
 7. The separator of claim 5, wherein said secondset of ribs are in a cross-machine direction relative to saidmicroporous membrane.
 8. The separator of claim 1, wherein saiduncross-linked or uncured rubber is impregnated into said microporousmembrane.
 9. The separator of claim 1, wherein said polyolefin is one ormore of the group consisting of polyethylene, polypropylene, highmolecular weight polyethylene (“HMWPE”), ultra-high molecular weightpolyethylene (“UHMWPE”), and combinations thereof.
 10. The separator ofclaim 9, wherein said microporous membrane comprises silica.
 11. A leadacid battery comprising: an electrolyte comprising one or morecontaminants, said one or more contaminants being one or more selectedfrom the group consisting of chromium, manganese, titanium, copper, andcombinations thereof; a microporous membrane comprising one or more ofthe group consisting of polyolefin, polyvinyl chloride (“PVC”),phenol-formaldehyde resins, uncross-linked or uncured rubber, nonwovenfibers, synthetic fibers, cellulosic fibers, and combinations thereof.12. The lead acid battery of claim 11, wherein said uncross-linkedrubber or uncured rubber being selected from the group consisting ofrubber latex, tire crumb, and combinations thereof.
 13. The lead acidbattery of claim 12, wherein said uncross-linked or uncured rubber is inan amount of no more than approximately 12% by weight of saidmicroporous membrane.
 14. The lead acid battery of claim 13, whereinsaid cross-linked rubber or uncured rubber is in an amount of at leastapproximately 2% by weight of said microporous membrane to approximately4% by weight of said microporous membrane.
 15. The lead acid battery ofclaim 11, wherein microporous membrane further comprises a first set ofribs on a first surface, and a second set of ribs on a second surface.16. The lead acid battery of claim 15 wherein said first set of ribs arein a machine direction relative to said microporous membrane.
 17. Thelead acid battery of claim 15, wherein said second set of ribs are in across-machine direction relative to said microporous membrane.
 18. Thelead acid battery of claim 11, wherein said uncross-linked or uncuredrubber is impregnated into said microporous membrane.
 19. The lead acidbattery of claim 11 wherein said polyolefin is one or more of the groupconsisting of polyethylene, polypropylene, high molecular weightpolyethylene (“HMWPE”), ultra-high molecular weight polyethylene(“UHMWPE”), and combinations thereof.
 20. The lead acid battery of claim19, wherein said microporous membrane comprises silica.
 21. The leadacid battery of claim 11, wherein the battery is a flooded lead acidbattery.
 22. The lead acid battery of claim 11, wherein the battery is adry charge flooded lead acid battery.
 23. In a dry charge flooded leadacid battery, the improvement comprising the separator of claim
 1. 24.In a flooded lead acid battery, the improvement comprising the separatorof claim 1.